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In the present article, we review the published formulae, summarize essential differences in participant sources, statistical methodologies, and predictive results. We argue that unrepresentative sampling and failure to use appropriate survival analysis methodology may have substantially biased much of the literature. We also explain why the survival analysis perspective is necessary if any such model is to undergo prospective validation. We use prospective diagnostic data from the PREDICT\u2010HD longitudinal study of CAG\u2010expanded participants to test conditional predictions derived from two survival models of AOO of HD. A prior model of the relationship of CAG and AOO originally published by Langbehn et al. yields reasonably accurate predictions, while a similar model by Gutierrez and MacDonald substantially overestimates diagnosis risk for all but the highest risk participants in this sample. The Langbehn et al. model appears accurate enough to have substantial utility in various research contexts. We also emphasize remaining caveats, many of which are relevant for any direct application to genetic counseling. \u00a9 2009 Wiley\u2010Liss, Inc.<\/jats:p>","DOI":"10.1002\/ajmg.b.30992","type":"journal-article","created":{"date-parts":[[2009,6,22]],"date-time":"2009-06-22T14:32:08Z","timestamp":1245681128000},"page":"397-408","source":"Crossref","is-referenced-by-count":337,"title":["CAG\u2010repeat length and the age of onset in Huntington disease (HD): A review and validation study of statistical approaches"],"prefix":"10.1002","volume":"153B","author":[{"given":"Douglas R.","family":"Langbehn","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Michael R.","family":"Hayden","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jane S.","family":"Paulsen","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"name":"and the PREDICT\u2010HD Investigators of the Huntington Study Group","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2010,2,18]]},"reference":[{"key":"e_1_2_7_2_1","first-page":"267","volume-title":"Second International Symposium on Information theory","author":"Akaike H","year":"1973"},{"key":"e_1_2_7_3_1","doi-asserted-by":"publisher","DOI":"10.1007\/978-1-4612-0919-5_38"},{"key":"e_1_2_7_4_1","first-page":"292","volume-title":"Survival analysis using the SAS system: A practical guide","author":"Allison PD","year":"1995"},{"key":"e_1_2_7_5_1","doi-asserted-by":"publisher","DOI":"10.1034\/j.1399-0004.2001.600305.x"},{"key":"e_1_2_7_6_1","doi-asserted-by":"publisher","DOI":"10.1136\/jmg.2006.045153"},{"issue":"3","key":"e_1_2_7_7_1","doi-asserted-by":"crossref","first-page":"293","DOI":"10.1111\/j.1469-1809.2006.00335.x","article-title":"The relationship between CAG repeat length and age of onset differs for Huntington's disease patients with juvenile onset or adult onset","volume":"71","author":"Andresen JM","year":"2007","journal-title":"Ann Hum Genet"},{"key":"e_1_2_7_8_1","doi-asserted-by":"publisher","DOI":"10.1038\/ng0893-398"},{"key":"e_1_2_7_9_1","doi-asserted-by":"publisher","DOI":"10.1001\/archneur.1996.00550120105023"},{"issue":"5","key":"e_1_2_7_10_1","first-page":"1202","article-title":"The likelihood of being affected with Huntington disease by a particular age, for a specific CAG size","volume":"60","author":"Brinkman RR","year":"1997","journal-title":"Am J Hum Genet"},{"key":"e_1_2_7_11_1","doi-asserted-by":"publisher","DOI":"10.1007\/978-1-4757-2917-7"},{"key":"e_1_2_7_12_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.pneurobio.2007.03.004"},{"key":"e_1_2_7_13_1","doi-asserted-by":"publisher","DOI":"10.1016\/S0304-3940(03)00436-1"},{"key":"e_1_2_7_14_1","volume-title":"SAS\/STAT 9.1: User's guide","author":"Clark V","year":"2004"},{"key":"e_1_2_7_15_1","first-page":"201","volume-title":"Analysis of survival data","author":"Cox DR","year":"1984"},{"key":"e_1_2_7_16_1","doi-asserted-by":"publisher","DOI":"10.1002\/ajmg.a.20190"},{"key":"e_1_2_7_17_1","doi-asserted-by":"publisher","DOI":"10.1038\/ng0893-387"},{"key":"e_1_2_7_18_1","doi-asserted-by":"publisher","DOI":"10.1086\/318193"},{"key":"e_1_2_7_19_1","volume-title":"Huntington's disease and insurance. 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